1. Field of the Invention
The present invention relates to an optical waveguide module, and more particularly to an optical waveguide module which has a semiconductor laser (laser diode), an optical waveguide that transmits a light signal from the laser diode to an optical fiber, and a photodiode that receives a light signal from the optical fiber via an optical waveguide.
2. Related Art
In recent years, communications means from trunk lines to subscribers is migrating from cables to optical communications at a rapid pace. Accompanying advancements in semiconductor technology, it has become possible to form a plurality of laser diode elements or photodiode elements on a single substrate, thereby facilitating the fabrication of optical components and optical communications equipment that can accommodate multiplexing. As a result, in order to achieve compactness and economy in optical modules used in optical subscriber systems, the mainstream approach has come to be one of using waveguides or the like to implement a transmitting/receiving module that integrates both a transmitting function and a receiving function (that is, an optical waveguide module).
While there are various types of optical waveguide modules, in a conventional optical transmitting/receiving module in which a transmitting photodiode is integrated with a receiving photodiode in a single optical module, the transmitted signal light of laser diodes that did not input to the optical waveguide acts as stray light that strikes a light-receiving photodiode, thereby becoming noise on the received signal light, which worsens the receiving sensitivity of the optical module.
In an optical module in which transmitting and receiving operations are performed by time division multiplexing, if a stray light that enters a light-receiving photodiode strikes a part other than the light-receiving surface of the photodiode, because the carrier diffusion time within the light-receiving photodiode is longer than the carrier diffusion time for carriers generated at the light-receiving surface, the noise has a long time constant, so that there is a worsening of receiving sensitivity immediately after switching from the transmitting operation to the receiving operation.
Because the laser diode stray light is guided as it experiences multiple reflections within the package, following a complex path of incidence before it strikes the photodiode, it is difficult to performing blocking so that stray light from the laser diode does not strike the
Accordingly, it is an object of the present invention to provide an optical waveguide module having a simple configuration, which enables blocking of light from a semiconductor laser so that it does not strike a light-receiving element.
In order to achieve the above-noted objects, the present invention adopts the following basic technical constitution.
Specifically, a first aspect of the present invention is an optical waveguide module in which transmitted signal light emitted from a laser light-emitting element 4 passes through a first optical waveguide 3a and a second optical waveguide 3b to strike a transmitting/receiving medium 5 such as an optical fiber, and a signal light from the transmitting/receiving medium 5 passes through the second optical waveguide 3b and is received by a light-receiving element 7, the optical waveguide module comprising, a first light-blocking resin covering part 12, which covers a light-emitting coupling part 11a coupling the laser light-emitting element 4 and the first optical waveguide 3a, and a second light-block resin covering part 14, which covers a light-receiving coupling part 13a coupling the light-receiving element 7 and the second optical waveguide 3b. 
In the second aspect of the present invention, the first and second light-blocking resin covering parts 12, 14 comprise a characteristic of either absorbing or reflecting light incident thereto.
In the third aspect of the present invention, the light-emitting coupling part 11a and the light-receiving coupling part 13a is filled with a transparent resin 11, 13, respectively.
In the fourth aspect of the present invention, the first light-blocking resin covering part 12 covers a monitoring light-receiving element 9 disposed at the rear part of the laser light-emitting element 4 and a monitoring light coupling part 11b coupling the laser light-emitting element 4 and the monitoring light-receiving element 9.
According to the above-noted configuration, of the transmitted signal light emitted from the laser light-emitting element, transmitted signal light that does not strike the first optical waveguide is blocked by the first light-blocking resin covering part, so that it does not leak to the outside. The light-receiving coupling parts are blocked by the second light-blocking resin covering part, thereby preventing the intrusion of externally introduced stray light into the light-receiving coupling parts. Therefore, because stray light from the laser light-emitting source does not find its way into the light-receiving element, noise caused by stray light does not occur, thereby preventing a worsening of the receiving sensitivity of the optical module.
In the fifth aspect of the present invention, a light-blocking plate 15, disposed above the first optical waveguide 3a, which blocks transmitted signal light 4a missing the light-emitting coupling part ha coupling the laser light-emitting element 4 and the first optical waveguide 3a.